Mechanics of granular materials: Constitutive behavior and pattern transformation
Başlık çevirisi mevcut değil.
- Tez No: 400024
- Danışmanlar: Belirtilmemiş.
- Tez Türü: Doktora
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2012
- Dil: İngilizce
- Üniversite: Technische Universiteit Delft (Delft University of Technology)
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 144
Özet
Özet yok.
Özet (Çeviri)
From pharmaceutical to mining or travelling desert dunes to earthquakes, granular materialsare at the heart of many industries and natural phenomena. Improving the efficiency of themachines, handling them or, constructing safer buildings requires a critical understanding oftheir behavior. However, this is not a straightforward task as opposed to what one might thinkdue to the abundance of particulate matter. From a fundamental point of view, it has beenonly recently realized that they cannot be easily classified as a solid or liquid or even a gas asthey are able to mimic all of these states under slightly different conditions. The challengeof the scientific research today, is to establish the link between the collective behavior andproperties of individual particles composing granular materials. Such a relation would enableto characterize them with only a few parameters in contrast to billions of particles typicallyfound in practice.In the first part of this thesis, we study the mechanical behavior of idealized disorderedsphere packings with discrete element simulations. The polydispersity and coefficient offriction of the particles are varied systematically to characterize their influence on the macroscopicstress-strain response. In isotropically deformed packings, the critical volume fractionmarking the transition from a solid to fluid like state increases with polydispersity, whereasit decreases with the coefficient of friction. The coordination number, i.e. average numberof contact per particle, is discontinuous at this density. During decompression it drops fromits isostatic value to zero and obeys a power law at higher volume fractions. The effectof polydispersity on the pressure is determined by the ratio of critical volume fraction andthe contact density which is equal to the trace of the fabric times a correction factor thatdepends only on the moments of the particle size distribution. Using the micromechanicaldefinition of the stress tensor, we derive an incremental constitutive model for the pressurewhich includes changes of fabric. With one fit parameter the linear regime of lower pressureis described, while with two parameters, the model captures well the non-linear pressureevolution in isotropically deformed polydisperse, frictionless and frictional packings.Anisotropic deformations are studied with triaxial test simulations. The shear strength ofthe packings is measured by the deviatoric stress ratio which first increases then saturateswith increasing particle coefficient of friction. Volumetric strain also depends on the particlefriction albeit in a non monotonic way. The maximum compaction after which packings startto dilate, is achieved at a relatively small coefficient of friction. The stress-strain responsedepends indirectly on the polydispersity which determines initial packing conditions. Wheninitially the volume fraction is fixed, the pressure as well as the shear strength decrease withpolydispersity. The opposite is observed when the initial pressure is imposed, although theeffect of polydispersity on the stress-strain behavior is less significant in this case. Finally, ahypoplastic constitutive model is calibrated with simulation results and the resulting materialcoefficients are related to particle properties.Most granular materials are amorphous and disordered as realized up to now. However, crystalstructures can be built by placing uniform particles on a regular lattice. The second partof the thesis is about pattern transformation in two-dimensional granular crystals composedof bi-disperse soft and hard cylindrical particles. We show with experiments and simulationsthat upon uniaxial compression the particles undergo structural rearrangements from an initialsquare to hexagon-like lattice. It is found that the characteristics of the transformationstrongly depend on the size ratio of the particles rather than their material properties. If theratio is small enough the transformation is homogeneous and practically reversible.The band structure of the granular crystal changes due to the pattern transformation. Usinga linearized contact force model, we compute the dispersion relation at different levels ofdeformation and show that band gaps open and close as the structure of the crystal changes.This could find applications in tunable acoustic devices such as filters or vibration isolators.In short, this thesis concerns the mechanics of granular materials subject to different modesof deformation. The constitutive behavior of disordered sphere packings and pattern transformationin regular arrays of cylinders have been studied.
Benzer Tezler
- Kaya dolgu yapılar ve kaya dolgulardaki son gelişmeler
Advances in rockfill structures
EKREM GENCO GÜNAY
- İki elastik katıdan oluşan bir sürekli ortamda yarı sonsuz bir yüzeye etki eden sinüzoidal yayılı yük için analitik bir çözüm
Analytical solution for a sinuzoidal distributed load acting on a semi infinite surface in a continuum of two elastic solids
NURİ KEREM BİNARK
Yüksek Lisans
Türkçe
2019
Makine Mühendisliğiİstanbul Teknik ÜniversitesiMakine Mühendisliği Ana Bilim Dalı
PROF. DR. MEHMET SALİH DOKUZ
- Nanoteknolojide eğri eksenli çubukların düzlem dışı davranışları için bir sonlu eleman formülasyonu
A finite element formulation for out of plane behavior of curved beams in nanotechnology
HİLAL KOÇ
Yüksek Lisans
Türkçe
2018
Makine Mühendisliğiİstanbul Teknik ÜniversitesiMakine Mühendisliği Ana Bilim Dalı
PROF. DR. EKREM TÜFEKCİ
- Geoteknik kıyı mühendisliğinde poroelastik deniz tabanı zemini-yapı sistemlerinin tekrarlı yükler altında sayısal modellenmesi
Numerical modeling of poroelastic seabed soil–structure systems under cyclic loading in geotechnical coastal engineering
ESRA TATLIOĞLU
Doktora
Türkçe
2018
İnşaat Mühendisliğiİstanbul Teknik Üniversitesiİnşaat Mühendisliği Ana Bilim Dalı
PROF. DR. MUSAFFA AYŞEN LAV
DOÇ. DR. MEHMET BARIŞ CAN ÜLKER
- Sathi kaplamalardaki kalıcı deformasyona etki eden parametrelerin incelenmesi
Investigating the parameters that affect permanent deformation (rutting) in chip-sealed pavements
VOLKAN EMRE UZ
Doktora
Türkçe
2012
UlaşımSüleyman Demirel Üniversitesiİnşaat Mühendisliği Ana Bilim Dalı
PROF. DR. MEHMET SALTAN